问题描述：
解释一句英文句子（需要生物学科学知识）
they then created a 'tetraploid' embryo by fusing two cells of an early-stage fertilized embryo.
后面fusing two cells of an early-stage fertilized embryo.
they then created a 'tetraploid' embryo by fusing two cells of an early-stage fertilized embryo.
后面fusing two cells of an early-stage fertilized embryo.
问题解答：
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